The present invention relates generally to the art of orthopae discs and more specifically to endoprosthesis of the body of the innominate bone.
The present invention can find application in surgical treatment of the dysplasia of the hip joint and its corollaries.
Known in the present state of the art are some endoprostheses of the body of the innominate bone, more exactly, those of the supra-acetabular region thereof which takes an immediate part in the formation of the cotyloid cavity. Dysplastic underdevelopment (also referred to as hypoplasia) manifests itself in deficiency of the osseous tissue for establishing the superior and anterior portions of the cotyloid cavity, or in a modified shape or position thereof which results in an incomplete or complete dislocation of thighbone and development of a dysplastic coxarthrosis.
At present the following endoprostheses of the body of the innominate bone are in common use: (a) made as a bony wedge (cf. USSR Inventor's Certificate No. 562,272); (b) in the shape of various visors (also named "sheds" in surgical practice). The prosthetic visors are in effect platelike autoplastic pedicellar grafts taken from the iliac bone and curved outwards, or rectangular or diamond-shaped unbound autohomoplastic bone grafts placed in a prepared fissure above the place of fixation of the joint capsule (cf. G. Castaing et G. Delplace "Techniques de la butee cotyloidienne", Rev. Chirurg. orthoped., vol. 62, May 1976, pp. 519 through 528), or else those curved approximately circularly lengthwise the bony plate, so that one of the longitudinal edges thereof is curved transversely inwards, while the opposite edge has fixing elements shaped as bearing surfaces provided with holes (cf. Application No. 2,410,057 field in the Federal Republic of Germany).
All the above-listed endoprostheses of the body of the innominate bone are instrumental in providing a support for the head of the femur whose surface is incongruent with that of the above head, while the load upon such a support exceeds its strength.
Another endoprosthesis of the body of the innominate bone is known (cf. USSR Inventor's Certificate No. 428,746) to comprise a visor curved longitudinally and transversely so as to form a concave surface which faces the head of the femur, and fixing elements of the visor which are made as a bearing surface with a supporting tooth, said surface being arranged at an angle to the visor and having holes for accommodating screws, thus establishing a cantilevered fixation.
The longitudinally-and-transversely curved visor is congruent with the head of the femur and is made fast on the innominate bone body, thus establishing a support for the head of the femur and compensating for a deficient osseous tissue in the superior portion of the cotyloid cavity.
The visor is fixed in position by screws and is reinforced by the supporting tooth.
The endoprosthesis described above fails, however, to compensate for completely the deficient osseous tissue in the bulk of the innominate bone body required for establishing the anterior and superior portions of the cotyloid cavity, thus not adding to the strength of the support for the head of the femur nor improving the congruence of the underdeveloped articular cavity with the head of the femur.
The cantilevered fixation of the visor results in slackening of the holding screws under dynamic loads, instability of the visor and loss of support for the head of the femur accompanied by an adversely affected congruence of the hip joint surfaces.